// This file is part of OpenTSDB.
// Copyright (C) 2010-2012  The OpenTSDB Authors.
//
// This program is free software: you can redistribute it and/or modify it
// under the terms of the GNU Lesser General Public License as published by
// the Free Software Foundation, either version 2.1 of the License, or (at your
// option) any later version.  This program is distributed in the hope that it
// will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty
// of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser
// General Public License for more details.  You should have received a copy
// of the GNU Lesser General Public License along with this program.  If not,
// see <http://www.gnu.org/licenses/>.
package net.opentsdb.core;

/**
 * A function capable of aggregating multiple {@link DataPoints} together.
 * <p/>
 * All aggregators must be stateless.  All they can do is run through a
 * sequence of {@link net.opentsdb.core.Aggregator.Longs Longs} or {@link net.opentsdb.core.Aggregator.Doubles Doubles} and return an
 * aggregated value.
 */
public interface Aggregator {

    /**
     * A sequence of {@code long}s.
     * <p/>
     * This interface is semantically equivalent to
     * {@code Iterator<long>}.
     */
    public interface Longs {

        /**
         * Returns {@code true} if this sequence has more values.
         * {@code false} otherwise.
         */
        boolean hasNextValue();

        /**
         * Returns the next {@code long} value in this sequence.
         *
         * @throws java.util.NoSuchElementException if calling {@link #hasNextValue} returns
         *                                          {@code false}.
         */
        long nextLongValue();

    }

    /**
     * A sequence of {@code double}s.
     * <p/>
     * This interface is semantically equivalent to
     * {@code Iterator<double>}.
     */
    public interface Doubles {

        /**
         * Returns {@code true} if this sequence has more values.
         * {@code false} otherwise.
         */
        boolean hasNextValue();

        /**
         * Returns the next {@code double} value in this sequence.
         *
         * @throws java.util.NoSuchElementException if calling {@link #hasNextValue} returns
         *                                          {@code false}.
         */
        double nextDoubleValue();

    }

    /**
     * Aggregates a sequence of {@code long}s.
     *
     * @param values The sequence to aggregate.
     * @return The aggregated value.
     */
    long runLong(Longs values);

    /**
     * Aggregates a sequence of {@code double}s.
     *
     * @param values The sequence to aggregate.
     * @return The aggregated value.
     */
    double runDouble(Doubles values);

}
